Hi Raka,
For open air use, I'd be looking at Qts values over 0.6 and maybe higher. Anything lower than that really needs an enclosure. A Qts of 0.707 would be optimally damped, higher values start bringing a "hump" in the response at resonance. You want to stay below 1.0 I would think.
-Chris
For open air use, I'd be looking at Qts values over 0.6 and maybe higher. Anything lower than that really needs an enclosure. A Qts of 0.707 would be optimally damped, higher values start bringing a "hump" in the response at resonance. You want to stay below 1.0 I would think.
-Chris
Hi Raka,
Do you mean Qms = 5? Qts is the total electrical / mechanical compostite. There is only so large a magnet that can be used to damp the cone, so at some point the mechanical Q will be so large that the total Q becomes over 1. At that point you are talking about electronic EQ and possibly motional feedback systems.
-Chris
Do you mean Qms = 5? Qts is the total electrical / mechanical compostite. There is only so large a magnet that can be used to damp the cone, so at some point the mechanical Q will be so large that the total Q becomes over 1. At that point you are talking about electronic EQ and possibly motional feedback systems.
-Chris
Hi Raka,
Okay, (0.35*5.00)/(0.35+5.00) is about 0.327. So Qts is 0.327. This speaker might be happy in a sealed box depending on it's Fs, or a ported box. In open air it would be overdamped I would think. I'd have to go back through my notes from years ago to see if those are reasonable figures or not for a speaker.
A speaker with a Qts of 0.383 is crying for a classic B4 ported alignment. Just as a point of reference.
-Chris
Okay, (0.35*5.00)/(0.35+5.00) is about 0.327. So Qts is 0.327. This speaker might be happy in a sealed box depending on it's Fs, or a ported box. In open air it would be overdamped I would think. I'd have to go back through my notes from years ago to see if those are reasonable figures or not for a speaker.
A speaker with a Qts of 0.383 is crying for a classic B4 ported alignment. Just as a point of reference.
-Chris
Well, a woofer with a Qts = 0.33 will be 9.6 dB down at Fs.
On the other hand, if Fs =20 Hz, and you were expecting the woofer to go down to only 50 Hz, that would seem to be okay. If I were going to go open baffle, I would purposely look for woofers with large Vas, since they would be more efficient for the same Qts and Fs than drivers with smaller Vas. And open baffle does not care about a driver's Vas.
Finally, I would point out that some years ago, Carver came out with an open baffle subwoofer for his ribbon speaker design. He purposely made the Qts of the drivers very, very high-like 2.0 or thereabouts-so that the peak in output would compensate for natural rolloff when the low bass notes come around from the back and cancel the front wave. I imagine he made the Vas very large as well, though I have no information on that.
On the other hand, if Fs =20 Hz, and you were expecting the woofer to go down to only 50 Hz, that would seem to be okay. If I were going to go open baffle, I would purposely look for woofers with large Vas, since they would be more efficient for the same Qts and Fs than drivers with smaller Vas. And open baffle does not care about a driver's Vas.
Finally, I would point out that some years ago, Carver came out with an open baffle subwoofer for his ribbon speaker design. He purposely made the Qts of the drivers very, very high-like 2.0 or thereabouts-so that the peak in output would compensate for natural rolloff when the low bass notes come around from the back and cancel the front wave. I imagine he made the Vas very large as well, though I have no information on that.
kelticwizard said:
That's the point I'm trying to investigate, but I'm not sure that an open baffle considers irrelevant the Vas data. For your information, my dipoles are almost finished and correctly equalized, I'm in the phase of listening to music, and get familiar with the things that do well (a lot) and the points to improve (not much
)In the typically used baffle sizes the excursion seems to be more important than Qts. I have seen quite a lot of dipole subwoofers here and in other forums, they typically work with drivers like Visaton TIW or Peerless XLS. Tymphany claim the LAT also works without baffle. It blows quite a lot of air without much excursion. Would be nice if someone found a theory that helps to choose baffle sizes. I only know a rule for very high Qts, very low excursion drivers.
Greets, Oliver
Greets, Oliver
It appears someone named Newman has done some investigation along these lines. Perhaps some member would be so kind as to Email the article over to you-I don't have it.
Reference to Newman article.
Reference to Newman article.
Thanks for the link, keltic, 'll try to get a copy of it.
Consort, wouldn't be it the other way around?
FWIW, here you have the distorsion graph of the 3 way dipoles. The mid driver is a 38l Vas. Don't trust the bass part, as I suspect the active filter is to blame of the most of it. I still have to check if there is interstage clipping. I don't have a calibrated mic, but the volume was double than for normal music.
Consort, wouldn't be it the other way around?
FWIW, here you have the distorsion graph of the 3 way dipoles. The mid driver is a 38l Vas. Don't trust the bass part, as I suspect the active filter is to blame of the most of it. I still have to check if there is interstage clipping. I don't have a calibrated mic, but the volume was double than for normal music.
Attachments
Vas does not matter for an open baffle.
Open baffles need a high Qts, as seen below a Qts of 1.5 still does not give a peak in the response. The image shows simulations of a"typical" open baffle with varying Qts values for the driver.
Open baffles need a high Qts, as seen below a Qts of 1.5 still does not give a peak in the response. The image shows simulations of a"typical" open baffle with varying Qts values for the driver.
An externally hosted image should be here but it was not working when we last tested it.
Raka:
Well, it looked like the woofers Carver used had a Qts of 3 instead of 2. Numbers you don't often see. that gives it a response at resonance, (25 Hz), of +9.5 dB!
Here is a discussion of the subject.
Also discussed is woofer by Lambda, a quality maker, and it's specs. The woofer is made especially for dipole use. Here are the specs:
Fs 21.66Hz
Vas 623L
Qms 15.16
Qes 1.002
Qts 0.94
Re 12.3 ohms
Impedance 16 ohms
Bl 12.26Tm
Mms 90g
1Wspl 90dB
xmax 13mm peak
voice coil height 12.4mm
air gap 38.4mm
Sd 855cm2
Pmax ~100W
This is surprising-a voice coil length of 12.4 mm and an air gap of 38.4 mm. It's an underhung voicecoil of +/- 12 mm excursion. Very unusual.
At any rate, note the Vas: 632 L, or 22.3 cu ft. While this speaker is not ncecessarily the last word in dipole design, it does show that a quality maker uses a very, very high Vas in designing for a dipole application.
Well, it looked like the woofers Carver used had a Qts of 3 instead of 2. Numbers you don't often see. that gives it a response at resonance, (25 Hz), of +9.5 dB!
Here is a discussion of the subject.
Also discussed is woofer by Lambda, a quality maker, and it's specs. The woofer is made especially for dipole use. Here are the specs:
Fs 21.66Hz
Vas 623L
Qms 15.16
Qes 1.002
Qts 0.94
Re 12.3 ohms
Impedance 16 ohms
Bl 12.26Tm
Mms 90g
1Wspl 90dB
xmax 13mm peak
voice coil height 12.4mm
air gap 38.4mm
Sd 855cm2
Pmax ~100W
This is surprising-a voice coil length of 12.4 mm and an air gap of 38.4 mm. It's an underhung voicecoil of +/- 12 mm excursion. Very unusual.
At any rate, note the Vas: 632 L, or 22.3 cu ft. While this speaker is not ncecessarily the last word in dipole design, it does show that a quality maker uses a very, very high Vas in designing for a dipole application.
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